Vehicle discharge lamp, vehicle discharge lamp device, lighting circuit combined type vehicle discharge lamp device, and lighting circuit

ABSTRACT

A mercury-free vehicle discharge lamp is described as including a discharge space with electrodes, wherein a spherical length b, which is a length in a tube axial direction of the light emitting part is 7.5 mm to 8.5 mm and a thickness volume V of the light emitting part is 50 mm 3  to 100 mm 3 , and wherein the following formula is satisfied: −20≦(a−35)×5.5+(x−13.5)×10 +(1.85−t)×100+(2.5−d)×100≦20, a: power W supplied in a stable lighting time, x: pressure [atm] of rare gas sealed in the discharge space ranging 10˜17 atm, t: thickness [mm] of a part where a wall with maximum thickness and ranging 1.30˜1.85 mm, and d: inner diameter [mm] of a part where the wall with maximum thickness.

TECHNICAL FIELD

The present invention relates to a vehicle discharge lamp used in aheadlight, etc., of an automobile, and to a so-called mercury-freedischarge lamp not utilizing mercury for discharge in a light emittingpart.

BACKGROUND ART

At present, a discharge lamp used as an automobile headlight, isdesigned to be lighted at about 35 W in a stable lighting time. Suchalighting condition is employed for achieving required total light flux,light distribution, and light emission efficiency, and also securingstable lighting. However, there is an increased market needs for anautomobile further improved in fuel efficiency, from a concern for aglobal environment. Further, electric vehicles and automobiles such as ahybrid car with low environmental load utilizing an electric motor as apower source, are popular and spread, and a reduction of powerconsumption is further strongly desired for on-vehicle lighting such asa headlight.

When a lighting power input into a lamp is only reduced, the total lightflux of the lamp is reduced accordingly and the light emissionefficiency is also reduced, and therefore an expected performance cannot be secured. Accordingly, development of a new lamp capable ofsatisfying the market needs even at a low power, is desired.

Regarding an automobile headlight for achieving a stable lighting at alow power of 15 to 30 W, Patent document 1 discloses a technique ofsolving the above-described problem by optimizing a sealed pressure inthe light emitting part and an inner diameter of the light emittingpart. However, sufficient light emission efficiency can not be obtainedonly by conditions provided by this document. Therefore, furtherimprovement is desired.

CITATION LIST

Patent Literature

-   -   PLT 1: Japanese Patent Application Laid-Open No. 2004-172056

SUMMARY OF THE INVENTION

Technical Problem

An object of the present invention is to provide a practical new vehicledischarge lamp capable of achieving required light emission efficiencyeven at a low power of 30 W or less.

Solution to Problem

The present invention provides a mercury-free discharge lamp, which is avehicle discharge lamp lighted stably at a power of 18 to 30 W in astable lighting time without substantially using mercury, including adischarge space which is defined in a light emitting part, into which adischarge medium containing metal halide and rare gas are sealed, and inwhich electrodes are arranged, satisfying the following formula 1.−40≦(a−35)×5.5+(x−13.5)×10+(1.85−t)×100+(2.5−d)×100≦40  (Formula 1)wherein

a: Power [W] supplied in the stable lighting time, satisfying 18≦a≦30

x: Pressure of the rare gas sealed in the discharge space [atm]

t: Thickness of a part where a wall thickness of the light emitting partis maximum [mm]

d: Inner diameter of a part where a wall thickness of the light emittingpart is maximum [mm]

Advantageous Effects of Invention

According to the present invention, various design conditions forachieving stable lighting at a low power, can be optimized by a simplemethod, and accordingly, a vehicle discharge lamp based on a desiredspecification can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view for explaining a discharge lamp according to a firstembodiment of the present invention.

FIG. 2 is an expanded partial sectional view of an essential part of thedischarge lamp shown in FIG. 1.

FIG. 3 is a view showing a relation between power supplied to a lamp,and light emission efficiency.

FIG. 4 is a view showing a relation between power at a lighting time anda temperature of an upper part of a light emitting part.

FIG. 5 is a view showing a relation between a temperature of the lightemitting part and the light emission efficiency.

FIG. 6 is a view showing a relation between a pressure of xenon sealedin the light emitting part, and the temperature of the light emittingpart.

FIG. 7 is a view showing a relation between an inner diameter of thelight emitting part of a part where a wall thickness of the lightemitting part is maximum, and the temperature of the light emittingpart.

FIG. 8 is a view showing a relation between a wall thickness of a partwhere the wall thickness of the light emitting part is maximum, and thetemperature of the light emitting part.

FIG. 9 is a table showing test results of a lamp with each parametervaried in accordance with a concept of the present invention, andevaluation of characteristics.

FIG. 10 is a view for explaining a discharge lamp according to a secondembodiment of the present invention.

FIG. 11 is a view for describing a distance c between a metal foil and ametal band, and a generation rate of a dielectric barrier discharge.

FIG. 12 is a view for describing a discharge lamp device according to athird embodiment of the present invention.

FIG. 13 is a view for explaining a circuit structure of the dischargelamp device.

FIG. 14 is a view for describing presence or absence of flickering whena current slope of a zero cross current is varied.

FIG. 15 is a current waveform chart for describing the zero crosscurrent.

FIG. 16 is an expanded view in the vicinity of the zero cross of FIG.15.

FIG. 17 is a view for describing presence or absence of the flickeringwhen a light frequency of the current in a stable time is varied.

FIG. 18 is a view for describing a lighting circuit combined typedischarge lamp device according to a fourth embodiment of the presentinvention.

FIG. 19 is a sectional view of the lighting circuit combined typedischarge lamp device of FIG. 18.

FIG. 20 is a view for describing a circuit structure of the lightingcircuit combined type discharge lamp device.

FIG. 21 is a view for describing the lighting circuit combined typedischarge lamp device according to a fifth embodiment of the presentinvention.

FIG. 22 is a view for describing a discharge lamp according to a sixthembodiment of the present invention.

FIG. 23 is a view for describing a startup voltage when a distance c′between the metal band and a conductive film is varied.

FIG. 24 is a view for describing the startup voltage when the distance cbetween the metal band and the metal foil is varied, and the distance c′between the metal band and the conductive film is varied.

FIG. 25 is an expanded view of the vicinity of a sealing part of thedischarge lamp of FIG. 22.

FIG. 26 is a view showing a relation between an area of a conductivecoating film and a drop rate of the startup voltage.

FIG. 27 is a view for describing other embodiment of the conductivecoating film.

FIG. 28 is a view for describing a discharge lamp according to a seventhembodiment of the present invention.

FIG. 29 is a view showing a relation between T1/T2 and the startupvoltage.

FIG. 30 is a view for describing other embodiment of the conductivecoating film.

FIG. 31 is a view for describing a discharge lamp according to an eighthembodiment of the present invention.

FIG. 32 is a view for describing other embodiment of the conductivecoating film.

FIG. 33 is a view for describing a discharge lamp according to a ninthembodiment of the present invention.

FIG. 34 is a view for describing a discharge lamp according to a tenthembodiment of the present invention.

FIG. 35 is a view for describing a discharge lamp according to aneleventh embodiment of the present invention.

FIG. 36 is a view for describing a variation of the startup voltage,when a high voltage pulse of negative polarity is applied to a lamp inwhich a conductive coating film is formed, or a high voltage pulse ofpositive polarity is applied thereto.

FIG. 37 is a view for describing a variation of the startup voltage,when a high voltage pulse of negative polarity is applied to a lamp inwhich a conductive coating film is not formed, or a high voltage pulseof positive polarity is applied thereto.

FIG. 38 is a view for describing the high voltage pulse with fall timeof about 300 ns.

FIG. 39 is a view for describing an applied high voltage pulse at thetime of carrying out both high voltage startup.

DESCRIPTION OF EMBODIMENTS

(First Embodiment)

An example of the embodiments of the present invention will bedescribed, with reference to FIG. 1 and FIG. 2. FIG. 1 is an overallview for describing an embodiment of a discharge lamp according to thepresent invention, and FIG. 2 is an expanded partial sectional view ofan essential part of the discharge lamp shown in FIG. 1, viewed from adifferent angle of about 90 degrees from FIG. 1.

The discharge lamp of this embodiment can be used as a light source ofan automobile headlight, and includes an elongated inner tube 1. Asubstantially elliptic hollow light emitting part 11 is formed in thevicinity of a center of the inner tube 1. Plate-like sealing parts 12formed by pinch seal, are formed on both ends of the light emitting part11, and cylindrical parts 14 are continuously formed on the both ends ofeach sealing part 12 via a boundary part 13. Note that the inner tube 1is preferably made of a material having heat resistant property andlight transmitting property, such as quartz glass. Further, the sealingpart 12 may have a cylindrical shape formed by shrink seal.

A discharge space 111 is formed in the light emitting part 11, with acenter having approximately a cylindrical shape, in such a manner asbeing tapered toward both ends. Volume of the discharge space 111 isgenerally 10 to 40 mm³ and particularly 20 to 30 mm³, when being usedfor the automobile headlight.

A discharge medium is sealed in the discharge space 111. At least ametal halide 2 and inert gas are contained in the discharge medium.

The metal halide 2 is made of halide of sodium, scandium, zinc, andindium. For example, iodine is used as halogen that constitutes themetal halide, although not limited thereto, and bromine and chlorine mayalso be used by combining them. Further, a combination of the metalhalide is not limited thereto, and halide of tin and cesium may bearbitrarily added. A sealing amount of the metal halide per unit volumemay be set to 0.008 to 0.016 mg/μl, for example.

For example, xenon is used as the inert gas sealed in the dischargespace 111. A sealed pressure of the inert gas can be adjusted accordingto a purpose of use. For example, in order to increase thecharacteristic of the total light flux, etc., the sealed pressure ispreferably set to 10 to 20 atm at a normal temperature (25° C.).Further, neon, argon, and krypton, etc., can be used other than xenon,and a mixed gas of combining them can also be used.

Wherein, the discharge medium not substantially containing mercury ispreferable. Regarding the description “without substantially usingmercury . . . ” in this specification should be interpreted as themeaning, without being limited to a case where an sealing amount ofmercury is 0 mg, including a case that the mercury is sealed with ansealing amount approximately equal to an amount almost not sealed,compared with a conventional discharge lamp having mercury therein, forexample, an amount of less than 2 mg per 1 ml, and preferably 1 mg orless.

Electrode mounts 3 are respectively air-tightly sealed to the sealingparts 12 formed on the both sides of the light emitting part 11. Eachelectrode mount 3 is constituted of a metal foil 31, an electrode 32, acoil 33, and a lead wire 34.

The metal foil 31 is a thin plate-like member made of molybdenum forexample.

The electrode 32 is a rod-like member constituted of so-called thoriatedtungsten obtained by, for example, doping tungsten with thorium oxide.One end thereof is welded to an end portion on the light emitting part11 side of the metal foil 31 in such a manner as being placed thereon,and the other end protrudes into the discharge space 111, with tip endsof the electrodes 32 face to each other while keeping a prescribeddistance therebetween. For example, each electrode 32 can be positionedin a range of 3.7 to 4.4 mm of the distance between the tip ends of theelectrodes 32, when observed through an outer tube 5, for the purpose ofuse for the automobile headlight for example. Note that a shape of theelectrode 32 is not limited to a straight rod shape with a diameterapproximately constant in a tube axial direction, and may be anon-straight-rod-like shape with a diameter of a tip end portion set tobe larger than a diameter of a base end portion, or may be a shape witha spherical tip end, and may be a shape with a diameter of one electrodeand a diameter of the other electrode different from each other like adirect-current lighting type. Further, an electrode material may be puretungsten, doped tungsten, and rhenium tungsten, etc.

For example, the coil 33 is a metal wire made of doped tungsten, and isspirally wound on an axis portion of the electrode 32 around the axis,the electrode 32 being air-tightly sealed to the sealing part 12. Thecoil 33 can be designed so that a coil wire diameter is set to 30 to 100μm, and a coil pitch is set to 600% or less.

The lead wire 34 is a metal wire made of molybdenum for example. An endof the lead wire 34 is connected to an end portion of the metal foil 31on a side far from the light emitting part 11 in such manner as beingplaced thereon, and the other end is extended approximately in parallelto a tube axis up to outside of the inner tube 1. For example, one endof an L-shaped support wire 35 made of nickel is connected by laserwelding, to the lead wire 34 extended to a front end side of the lamp,namely, to a side far from a socket 6. For example, a sleeve 4 made ofceramics is mounted on a part of the support wire 35 extending inparallel to the inner tube 1.

The cylindrical outer tube 5 is concentrically provided to outside ofthe inner tube 1 thus constructed, so as to cover the light emittingpart 11. Such connection between the inner and outer tubes is made bywelding both ends of the outer tube 5 to the vicinity of the cylindricalpart 14 of the inner tube 1. Gas is sealed in a closed space 51 formedbetween the inner tube 1 and the outer tube 5. As such gas, dielectricbarrier discharge gas, and for example, one kind of gas selected fromneon, argon, xenon, and nitrogen, or mixed gas thereof can be used. Apressure of the gas is preferably set to 0.3 atm or less, andparticularly 0.1 atm or less. The outer tube 5 is preferably formed by amaterial having thermal expansion coefficient close to that of the innertube 1, and having UV-blocking property. Then, quartz glass added withoxide such as titanium, cerium, and aluminum can be used for the outertube 5.

The socket 6 is connected to one end of the inner tube 1 to which theouter tube 5 is connected. Such a connection is made by mounting a metalband 71 on an outer peripheral surface of the outer tube 5, and graspingthe metal band 71 by metal ligulas 72 which are formed so as to protrudefrom the socket 6. Further, a bottom terminal 81 is formed on a bottomof the socket 6, and a side terminal 82 is formed on a side portionthereof, and the lead wire 34 and the support wire 35 are connected tothe bottom terminal 81 and the side terminal 82.

The discharge lamp thus constructed is connected to a lighting circuit(see FIG. 13) so that the bottom terminal 81 is positioned on a higherpressure side, and the side terminal 82 is positioned on a lowerpressure side. When being used as the automobile headlight, thedischarge lamp is attached and lighted, so that the tube axis of thelamp is set in approximately a horizontal state, and the support wire 35is positioned in a lower part.

In a conventional mercury-free discharge lamp, total light flux of 3200lm is obtained by lighting at a power of 35 W in a steady time. Thelight emission efficiency calculated therefrom is about 911 m/W.However, as described above, when the power applied to the lamp issimply reduced, the light emission efficiency is reduced accordingly(FIG. 3).

As a result of strenuous efforts and study by inventors of the presentinvention, it is found that there is a relevance between the lightemission efficiency of the lamp and the temperature of the lightemitting part. FIG. 4 is a graph for plotting the test results, withpower input into the lamp during lighting taken on a horizontal axis,and the temperature of the light emitting part taken on a vertical axis.It is found from this graph that the temperature of the light emittingpart is reduced when the power of the lamp is reduced. Note that thetemperature of the light emitting part called here, can be obtained bymeasuring the temperature of an upper side part of the light emittingpart 11 on a paper face of FIG. 1. In FIG. 1, when the lamp is lighted,with the sleeve 4 placed downward as shown in FIG. 1, an arc isgenerated between the electrodes so as to be warped upward. Therefore,an increase of the temperature in an upper part of the light emittingpart is remarkable, if compared with a lower part.

Further, explanation will be given for the relation between a variationof the temperature of the light emitting part and the light emissionefficiency, with reference to FIG. 5. FIG. 5 shows the results ofcalculating the light emission efficiency [lm/W] when the temperature ofthe light emitting part is varied, with 920° C. as a reference, when thelamp is lighted at 35 W. As is clarified from this graph, a correlationis recognized, such that the light emission efficiency is reduced whenthe temperature of the light emitting part is reduced. It appears thatthis is because by reducing the temperature of the light emitting part,a partial pressure of the metal halide sealed in the light emitting partis also reduced.

As described above, it is found that the correlation is establishedbetween the temperature of the light emitting part and the lightemission efficiency of the lamp. In other words, such knowledge suggestsa point that the light emission efficiency can be controlled in adesired range, by appropriately adjusting the temperature of the lightemitting part.

By focusing on a control of the temperature of the light emitting part,various parameters for designing the lamp having a sufficient lightemission efficiency even under a low power condition, will bespecifically described hereafter based on the present invention.

(1) Sealed Pressure of Xenon

FIG. 6 is a graph showing a variation amount (920° C. set as areference) of the temperature of the light emitting part, when sealedpressure of xenon at room temperature is increased or decreased, with13.5 atm as a reference. As is clarified from this graph, the relationbetween the sealed pressure of xenon and the variation amount of thetemperature is set in approximately a proportional relationship, whereinthe temperature of the light emitting part is increased as the xenonsealed pressure is increased. The xenon sealed pressure can be obtainedby collecting xenon gas by destroying the light emitting part in thewater, and measuring this amount.

Note that the xenon sealed pressure 13.5 atm used as a reference in FIG.6, and the temperature of the light emitting part 920° C. are given asembodiments of the reference simply for the convenience of theexplanation, and for example such specific physical amount is notnecessarily suitable in relation to the present invention.

Namely, these values are arbitrarily defined reference values for theconvenience of the explanation, including the reference values of otherparameters described below, and restricted interpretation of the rangeof the present invention should be avoided by these reference values.

(2) Inner Diameter of the Light Emitting Part

FIG. 7 is a graph showing relative values based on the inner diameter ofthe light emitting part 2.5 mm taken on the horizontal axis, and showingrelative values based on the temperature of the light emitting part 920°C. taken on the vertical axis. The “inner diameter of the light emittingpart” in this specification means a diameter of a part where the wallthickness of the light emitting part 11 shown by designation mark “d” inFIG. 2, is maximum, unless particularly defined otherwise. Also, it isfound from the graph shown in FIG. 7, that the temperature of the lightemitting part is increased when the inner diameter of the light emittingpart is decreased. This is because when the inner diameter of the lightemitting part is decreased, a distance up to the arc generated betweenthe electrodes is also decreased, thus remarkably increasing thetemperature.

(3) Wall Thickness of the Light Emitting Part

FIG. 8 is a graph showing relative values based on the wall thickness ofthe light emitting part 1.85 mm taken on the horizontal axis, andrelative values based on the temperature of the light emitting part 920°C. taken on the vertical axis. The “wall thickness of the light emittingpart” in this specification means a thickness of a part where the wallthickness of the light emitting part 11 shown by designation mark “t” inFIG. 2 is maximum, unless particularly defined otherwise. It is foundfrom the graph shown in FIG. 8, that the temperature of the lightemitting part is increased when the wall thickness of the light emittingpart is decreased. This is because when the wall thickness of the lightemitting part is decreased, heat is hardly diffused, thus causing atemperature increase to occur locally.

The wall thickness and the inner diameter of the light emitting part canbe measured by using a publicly-known measuring device such as an X-raydiffraction device.

In order to examine characteristics of the lamp in which the temperatureof the light emitting part is adjusted by varying the parameters of theaforementioned (1) to (3), a characteristic test was carried out, usinga vehicle discharge lamp of the following specification as a basicdesign.

The light emitting part, with inner diameter d of 2.2 mm; outer diameterof 5.2 mm; wall thickness t of 1.5 mm; spherical body length b of 7.8mm; thickness volume V of 89.5 mm³, and volume of the discharge space of20 mm³, was used. The metal halide sealed in the discharge space wascomposed of a mixture of scandium iodide, sodium iodide, zinc iodide,and indium bromide, and total sealing amount was 0.2 mg. The ratio ofthe sealing amount of each metal halide wasScI3:NaI:ZnI2:InBr=1.00:1.50:0.40:0.01 by weight ratio. Then, 13.5 atmof Xenon was sealed as rare gas.

The electrode made of thoriated tungsten including 0.5 wt % of thoriumoxide, with axial length of 7.5 mm, electrode diameter of 0.33 mm, andinter-electrode distance of 3.9 mm, was used. Further, the metal foilmade of molybdenum with thickness of 20 μm, width of 1.5 mm, and tubeaxial direction length of 6.5 mm, was laser-welded to one end of theelectrode, and was air-tightly sealed to a thin plate-like sealing partwith thickness of 2.8 mm and width of 4.1 mm, so that a coil with pitchof 200% was wound on an about half of the region of an electrode axispositioned in the sealing part. The outer tube that surrounds the innertube is formed into a cylindrical shape made of quartz glass doped witha material for blocking UV-light, with inner diameter of 7.0 mm and wallthickness of 1.0 mm. Argon of 0.05 atm was sealed in a closed spacesurrounded by the outer tube and the inner tube. Further, a distancebetween a part where the wall thickness of the light emitting part wasmaximum and the inner surface of the outer tube, was set to 0.95 mm fora portion to be an upper side when arranged in a horizontal direction,and set to 0.85 mm for a portion to be a lower side when arranged in ahorizontal direction.

With this specification, about 2000 lm was obtained by an input at 25 W.

Further, regarding the parameters of (1) to (3), the following matterswere clarified and therefore a range of numerical values to be testedand evaluated was limited.

First, when the sealed pressure of xenon of (1) is less than 10 atm at aroom temperature, the light flux at the time of starting the lamp cannot be obtained, and this is not suitable for the automobile headlight.Further, when the xenon sealed pressure exceeds 17 atm, excessive loadis added to the sealing part, thus posing a problem like a failure inlighting the lamp due to leak of the current. Therefore, in this test,the xenon sealed pressure was adjusted step by step in a range of 10 to17 atm.

When the inner diameter of the light emitting part of (2) is set to besmaller than 2.0 mm, a light shielding action of the sealed metal halideis remarkably exhibited, thus reducing the light emission efficiency.Further, when the inner diameter is set to be larger than 2.5 mm, thereis a possibility that the light emitting part is brought into contactwith the outer tube, depending on manufacturing variation, and alsodepending on the wall thickness of the light emitting part, when aspecification is similar to the specification of a conventional lampthat is lighted at 35 W, and therefore a manufacturing yield isdeteriorated. Accordingly, the test was carried out, with the innerdiameter of the light emitting part adjusted in a range of 2.0 to 2.5mm.

When the wall thickness of the light emitting part of (3) is set to besmaller than 1.30 mm, there is a possibility that the light emittingpart is remarkably expanded. Further, when the wall thickness is set tobe larger than 1.85 mm, there is a possibility that the outer tube andthe light emitting part are brought into contact with each other,although depending on the inner diameter of the light emitting part, andthis is not preferable. Accordingly, in this test, the wall thickness ofthe light emitting part was adjusted in a range of 1.30 to 1.85 mm.

Results of the test carried out under the aforementioned conditions andcharacteristic evaluation are shown in FIG. 9. “◯” in the item of“judgment” means the lamp showing excellent characteristic, and “x”indicates a defective lamp. Further, “Δ” indicates a combination ofthem, wherein total light flux is reduced because input power isreduced, although light emission efficiency is obtained.

It is found that an excellent result can be obtained regarding startupcharacteristic and service life characteristic, by controlling thetemperature of the light emitting part within ±40° C., compared with thepresent lamp that is lighted at 35 W. Namely, sufficient light emissionefficiency can not be obtained when the relative temperature of thelight emitting part is lower than −40° C. compared with the lamp lightedat 35 W, and such a lamp is outside a practical range. Further, when therelative temperature exceeds 40° C., the light emitting part becomesclouded, thus involving a problem that usable total light flux isreduced, and shortening a service life of the lamp. It was found fromthis result, that excellent characteristic was exhibited by thedischarge lamp if satisfying the following formula 1.−40≦(a−35)×5.5+(x−13.5)×10+(1.85−t)×100+(2.5−d)×100≦40  (Formula 1)

wherein

a: power [W] supplied in a stable lighting time, satisfying 18≦a≦30

x: pressure of xenon sealed in the discharge space [atm]

t: thickness of a part where the wall thickness of the light emittingpart is maximum [mm]

d: inner diameter of a part where the wall thickness of the lightemitting part is maximum [mm]

The formula 1 is obtained by mathematizing the following mater. Namely,excellent results are shown if the temperature of the light emittingpart is in a range of ±40° C. compared with a conventional one.Specifically, a numerical value of a left side corresponds to −40° C.,being a lower limit value of an allowable temperature, and a numericalvalue of a right side corresponds to 40° C., being an upper limit valuethereof. Then, the item of a middle side [(a−35)×5.5] corresponds to thevariation amount of the temperature of the light emitting part, which isvaried depending on a power of the lamp, and the item of [(x−13.5)×10]corresponds to the variation amount of the temperature of the lightemitting part, which is varied depending on the sealed pressure ofxenon. Also, the item of [(1.85−t)×100] corresponds to the variationamount of the temperature of the light emitting part, which is varieddepending on the wall thickness of the light emitting part, and the itemof [(2.5−d)×100] corresponds to the variation amount of the temperatureof the light emitting part, which is varied depending on the innerdiameter of the light emitting part.

By employing this inequality based on the present invention, thedischarge lamp having sufficient startup characteristic and service lifecharacteristic can be designed even at a lower power of 18 to 30 W.

Application of the present invention will be described next, in a casethat further detailed conditions are set. Explanation is given above,such that the aforementioned formula 1 can be applied to the lamp with apower in a range of 18 to 30 W, which is evaluated to be a lower power.However, even if the light emission efficiency can be improved to beequal to or more than the power of the lamp, low power of the lamp meansthat the total light flux is also reduced by a portion of the low power((total light flux)=(lamp power)×(light emission efficiency)).Accordingly, the light emission efficiency required for achievingpractical total light flux of 1800 to 2200 lm is different between lamppowers 18 W and 30 W. For example, in order to obtain the light flux of2000 lm at an input power of 20 W for example, efficiency of 100 lm/W isrequired. This is because efficiency higher than the efficiency of thepresent lamp of 35 W (911 m/W) is required, and in other words, highertemperature of the light emitting part is necessary.

Accordingly, when the lamp power is 18 to 22 W, an optimal relation ofeach parameter can be expressed by the following formula 2.20≦(a−35)×5.5+(x−13.5)×10+(1.85−t)×100+(2.5−d)×100≦40  (Formula 2)

wherein

a: Power supplied in a stable lighting time, satisfying 18≦a≦22 [W]

x: Pressure of rare gas sealed in the discharge space [atm]

t: Thickness of a part where the wall thickness of the light emittingpart is maximum [mm]

d: Inner diameter of a part where the wall thickness of the lightemitting part is maximum [mm]

When the lamp power is 22 to 26 W, the light emission efficiency needsto be controlled to the same degree of the conventional lamp of 35 W.Therefore, the relation of each parameter can be expressed by thefollowing formula 3.−20≦(a−35)×5.5+(x−13.5)×10+(1.85−−t)×100+(2.5−d)×100≦20  (Formula 3)

wherein

a: Power supplied in a stable lighting time, satisfying 22<a≦26 [W]

x: Pressure of rare gas sealed in the discharge space [atm]

t: Thickness of a part where the wall thickness of the light emittingpart is maximum [mm]

d: Inner diameter of a part where the wall thickness of the lightemitting part is maximum [mm]

when the lamp power is 26 to 30 W, the light emission efficiency needsto be controlled to about 70 lm/W, and therefore the relation of eachparameter can be expressed by formula 4.−40≦(a−35)×5.5+(x−13.5)×10+(1.85−−t)×100+(2.5−d)×100≦−20  (Formula 4)

wherein a: Power supplied in a stable lighting time, satisfying 26<a≦30[W]

x: Pressure of rare gas sealed in the discharge space [atm]

t: Thickness of a part where the wall thickness of the light emittingpart is maximum [mm]

d: Inner diameter of a part where the wall thickness of the lightemitting part is maximum [mm]

As described above, one of the major objects of the present invention isto obtain the total light flux of 2000±200 lm at an input power of 18 to30 W. However, it should be understood that such a numerical value rangeof the input power and the total light flux also includes a rangedetermined depending on a manufacturing variation and a use state, as anequivalent.

In addition, in the discharge lamp that is lighted at a power lower thana conventional power, the thickness volume V of the light emitting part11 is preferably set in a suitable range, to keep the temperature of thelight emitting part suitably. This is because the temperature of a lightemitting tube is most influenced by the inner diameter d of a part wherethe wall thickness is maximum, and the thickness t, and the temperatureof the light emitting part is influenced by the spherical body length band shapes of the light emitting part 11 and the discharge space 111.Then, it is found that the thickness volume V of the light emitting part11 is preferably set in a suitable range similarly to the wall thicknesst, the inner diameter d, and the spherical body length b. For example,124.5 mm³, being a conventional thickness volume V of the light emittingpart 11, and 89.5 mm³, being the thickness volume V of the embodiment,are greatly different characteristics. As a result of the test by theinventors of the present invention, it is found that preferably the wallthickness t is set to 1.30 to 1.85 mm, the inner diameter d is set to2.0 to 2.5 mm, the spherical body length b is set to 7.5 mm to 8.5 mm,and the thickness volume V of the light emitting part 11 is set to 50mm³ to 100 mm³, and preferably set to 60 mm3 to 90 mm³. Note that thethickness volume V of the light emitting part 11 can be calculated bycutting a boundary between the light emitting part 11 and the sealingpart 12, and measuring a weight of the remained light emitting part 11,and thereafter dividing the measured weight by a relative weight of amaterial of the light emitting part 11 (for example, the relative weightof the quartz glass is 2.65 g/cm³).

Further, the electrode 32 is preferably made of thoriated tungsten. Thisis because the electrode not including thorium oxide, has a highworkfunction, thus making it difficult to increase the efficiency. Thecontent is preferably 0.1 wt % or more and 0.5 wt % or less, whensuppressing effect of flickering and efficiency are taken intoconsideration.

Further, the gas sealed into the closed space 51 is also preferablytaken into consideration. Namely, the light emission efficiency and alight flux maintenance factor in FIG. 9 are influenced by the gas sealedinto the closed space 51, depending on a heat conductivity of the gas ofthe closed space 51. When a test was carried out by the inventors of thepresent invention, it was found that in the discharge lamp of low power,if a single gas is used, generally it is easier to keep the temperatureof the light emitting part by argon (λ=0.0177 W/m·K) than sealednitrogen which is generally sealed in a case of the conventional lamp of35 W. In a case of a mixed gas mixing argon, neon (λ=0.0493 W/m·K),xenon (λ=0.0057 W/m·K), and nitrogen (λ=0.0260 W/m·K), etc., heatconductivity λ is preferably 0.010 to 0.030 W/m·K, and furtherpreferably 0.015 to 0.021 W/m·K. Note that the heat conductivity λ ofthe mixed gas is obtained in such a manner that the heat conductivityspecific to gas is multiplied by the sealing ratio for each gas, andmultiplied values thus obtained are totaled.

Further, the temperature of the light emitting part is also influencedby a distance D between a part where the outer diameter of the lightemitting part 11 is maximum and an inner surface of the outer tube 5,similarly to the heat conductivity λ of the gas. According to the testby the inventors of the present invention, it was found that thedistance D was longer than about 0.3 mm, being a general distance, andwas preferably 0.5 to 1.0 mm, and further preferably 0.65 to 0.85 mm.Note that as shown in FIG. 2, the light emitting part 11 is offsetdownward with respect to the tube axis of the outer tube 5 in ahorizontal state, and a distance in an upper part of the light emittingpart may be set to be larger by about 1 mm than a distance in a lowerpart thereof.

(Second Embodiment)

FIG. 10 is a view for describing a vehicle discharge lamp according to asecond embodiment of the present invention. Regarding each part of theembodiment, the same signs and numerals are assigned to a part same aseach part of the vehicle discharge lamp of the first embodiment, andexplanation thereof is omitted.

In this embodiment, a position for mounting the metal band 71 is set atthe light emitting part 11 side, rather than the position shown in thefirst embodiment. Thus, a total length of the discharge lamp can beshortened, and therefore a compact lamp can be realized. Note that inthis embodiment, in accordance with a change of a position of the metalband 71, a position of a heat sealing part is changed to a tip end sideof the lamp closer thereto than conventional, without changing a lengthbetween the heat sealing part on the socket 5 side of the inner tube 1and the outer tube 5. Therefore, the lamp can be held without changing astructure of the socket 5.

Further, in this lamp, the distance c between the metal foil 31 and themetal band 71, namely, a length in the tube axial direction from an endportion of the metal band 71 on the tip end side of the lamp, to thesocket 5 side end portion of the metal foil 31 is shortened. Therefore,a generation rate of the dielectric barrier discharge is improved toassist start of the lamp at startup, and an advantage of an excellentstartup performance can be obtained.

FIG. 11 is a view showing results of testing the generation rate of thedielectric barrier discharge, regarding 50 lamps respectively, withdistance c varied between the metal foil and the metal band. As isclarified from this figure, the generation rate of the dielectricbarrier discharge is higher as the distance c becomes shorter, and forexample, the dielectric barrier discharge is tremendously easilygenerated at distance c=0.5 mm of this embodiment, compared with aconventional case of 5.5 mm. The reason can be considered as follows.Namely, the distance for generating the dielectric barrier discharge isshortened when the distance c is closed to 0. According to the resultsof the test, when the distance c is set to 2 mm or less, andparticularly the distance c is set to 0 mm or less, namely, when atleast a part of the metal foil 31 and a part of the metal band 71 areoverlapped on each other, a high effect can be expected.

Such an effect of increasing the generation rate of the dielectricbarrier discharge at startup, can be similarly obtained even by a metalmember such as a metal plate or a metal film having conductivity.However, it is most efficient that the metal band 71 for connecting alamp portion and a socket portion has a function of assisting thegeneration of the dielectric barrier discharge, as shown in thisembodiment.

(Third Embodiment)

FIG. 12 is a view for describing a vehicle discharge lamp deviceaccording to a third embodiment of the present invention, and FIG. 13 isa circuit view.

The vehicle discharge lamp device is constituted of a vehicle dischargelamp 101, a reflector 102, a light shielding control plate 103, a lens104, and a lighting circuit 105, and is used, with a tube axis set inapproximately a horizontal state.

The vehicle discharge lamp 101 is the lamp described in the firstembodiment, etc.

The reflector 102 is a parabolic shaped metal member provided forreflecting lights frontward, the lights being generated by the vehicledischarge lamp 101. An opening is formed in the vicinity of its center,and a front end portion of the socket 6 of the vehicle discharge lamp101 is fixed to the opening end, so that the light emitting part 11 ispositioned inside of the reflector 102.

The light shielding control plate 103 is the metal member provided forforming a light distribution called a outline. The light shieldingcontrol plate 103 is a movable type, and switch to a high beam from alow beam is enabled by making the light shielding control plate 103inclined frontward to a bottom side.

The lens 104 is a convex lens provided for forming a desired lightdistribution by collecting the lights reflected by the reflector 102,and is disposed in the opening on the tip end side of the reflector 102.

The lighting circuit 105 is a circuit for starting and lighting thevehicle discharge lamp 101, and as shown in FIG. 13, includes an ignitercircuit 1051 and a ballast circuit 1052 wherein DC power DS such as abattery and switch SW are connected to an input side, and the vehicledischarge lamp 101 is connected to an output side.

The igniter circuit 1051 is a circuit for starting the vehicle dischargelamp 101 by causing dielectric breakdown to occur between a pair ofelectrodes 32, by generating a high-voltage pulse of about 30 kV andapplying it to the lamp. The igniter circuit 1051 is also constituted ofa transformer, a capacitor, a gap, and a resistor, etc.

The ballast circuit 1052 is a circuit for keeping the lighting of thevehicle discharge lamp 101 started by the igniter circuit 1051. Theballast circuit 1052 is also constituted of a DC/DC converter circuit,DC/AC converter circuit, a current/voltage detecting circuit, and acontrol circuit, etc.

As is described in patent document 1, a discharge lamp with a lowerpower has a problem that flickering occurs due to reduction of a currentvalue, and as a result of flickering, fizzle-out is easily generated.The patent document 1 provides the invention of suppressing the problemof flickering by more thinly designing an electrode than conventional.An effect of suppressing the flickering in a steady time can be expectedif this invention is employed. However, as a result of examination bythe inventors of the present invention, it is found that in a lamp intowhich, for example, 2.0 A of current which is more than three times thecurrent of a steady time, is input at startup for 5 or more to quickenrise of light flux, the temperature is excessively high at a startuptime in a case of a thin electrode, and such a lamp has a short servicelife. Namely, in the means of the patent document 1, it is difficult torealize the vehicle discharge lamp with lower power, a long servicelife, and a quick rise of light flux, wherein flickering is hardlygenerated.

Therefore, when the means for suppressing the flickering is examined byusing other device, it is found that a low power discharge lamp hardlyallowing flickering to occur can be realized by suitably setting acurrent slope of a zero cross current in a steady time set by theballast circuit 1052, even under a condition that a currentcross-sectional area is 6 to 15 A/mm² (a diameter of the electrodecorresponds to about 0.25 to 0.35 mm. Note that the diameter in a caseof the electrode having partially different size, is a diameter of aportion occupying a major part of the electrode), capable ofwithstanding a large current if such a current is input.

FIG. 14 is a view for describing presence/absence of the flickering whenthe current slope of the zero cross current is varied. Wherein, the“current slope of the zero cross current” means the current slope whenthe polarity of the current in a steady time is changed, namely, thecurrent slope after a current value crosses the 0 A horizontal axis. Thecurrent slope is expressed by values in a period from a point where thepolarity is inverted with great influence on suppression of theflickering, up to 0.2 A. For example, in FIG. 16, which is an expandedview of the vicinity of the zero cross of FIG. 15, the current slope ofthe zero cross current is 0.062 A/μs. Further, in this test, the powerwas set to 25 W, and the flickering was judged by measuring with anilluminometer a brightness of 60 to 720 seconds after lighting, and itwas judged to be x when there was a variation of the brightness of 3% ormore, with respect to the brightness of 0.5 seconds before.

As a result, it is found that there is a relation between the currentslope of the zero cross current and the flickering, and although theflickering is not generated at 0.05 A/μs or more, the flickering isgenerated when the current slope of the zero cross current is 0.03 A/μs.It can be considered that this is because when the current slope of thezero cross current is 0.03 A/μs or less, the current does not flow tothe electrode so much immediately after inverting the polarity, thusreducing the temperature of the electrode, resulting in unstablestarting point of arc. Meanwhile, when the current slope of the zerocross current is 0.05 A/μs or more, the temperature of the electrode isnot decreased even if the polarity is inverted, thus making it possibleto keep a high temperature, and hardly allowing the flickering to occur.Accordingly, the current slope of the zero cross current is preferablyset to 0.05 A/μs or more. Note that as the current slope of the zerocross current is larger, there is an effective advantage against theflickering. However, the current slope of the zero cross current isadjusted, mainly by reducing the number of turns of a secondary windingof a transformer. Therefore, practically, the current slope of the zerocross current is preferably set to 0.60 A/μs or less.

In addition, it is further effective to set a lighting frequency in asuitable range. Specifically, as shown in FIG. 17, when the frequency is500 Hz or less, the temperature of the electrode is kept to be high, andtherefore the flickering is suppressed. However, when the frequency is100 Hz or less, the temperature of the electrode becomes unnecessarilytoo high, resulting in a short service life. Therefore, the frequency ispreferably set to 20 to 500 Hz.

(Fourth Embodiment)

FIG. 18 is a view for describing a lighting circuit combined typevehicle discharge lamp device according to a fourth embodiment of thepresent invention, and FIG. 19 is a sectional view of FIG. 18.

The aforementioned embodiment is a type that a lamp portion and acircuit portion are handled as separate bodies. However, this embodimentis a type that the lamp portion and the circuit portion are integrallyformed. Namely, a burner BN of the lamp and a circuit part CR includingthe igniter circuit and the ballast circuit are integrally formed.

The circuit part CR is a device for starting and stably lighting theburner BN, and includes a case 91 made of PPS resin for example, as ahousing. The case 91 is constituted of a main body part 911 and a lidmember 912 which are engaged with each other.

The main body part 911 has a socket part 9111 on its front end side, andthe burner BN is held by the socket part 9111 as follows. Namely,similarly to the first embodiment, the metal band 71 is mounted on theouter peripheral surface of the outer tube 5, and the metal band 71 isgrasped by the metal ligulas 72 which are protruded from the socket part9111.

Further, space is formed inside the main body part 911. The space isfurther divided into an upper space 921 and a lower space 922, by aspace dividing wall 9112 formed inside the main body part 911 along atube axial direction. Note that although the space dividing wall 9112 isintegrally formed with the main body part 911 of the case 91 in thisembodiment, a separately formed wall may be formed by inserting it intothe main body part 911 from a rear side, or may be formed, with acontainer used as a wall, in which a transformer 931 as will bedescribed later is housed.

The transformer 931 is disposed on the front end side of the upper space921 of the case 91. The transformer 931 is formed by winding a primarywinding and the secondary winding on an elongated rod-like iron core,and is used in a state of being housed in the container filled with aninsulating material such as epoxy, for securing insulation properties.However, the shape of the transformer 931 is not limited to a rod-likeshape, and of course there is no problem in forming it into a box shapeor a donut shape. A high-voltage terminal 913 is provided to thetransformer 931, and the high-voltage terminal 913 is connected to alead 34 led out into an internal space of the main body part 911. Thisconnection part is a part into which a high-voltage pulse is input atstartup, and therefore as shown in FIG. 19, preferably the space ispotted with an insulating material, or a resin wall is newly formed, forsecuring the insulation properties.

Further, a first circuit element group 932 is arranged on a rear endside of the upper space 921, for generating the high-voltage pulse bythe transformer 931 to start the burner BN. The first circuit elementgroup 932 is constituted of a capacitor, a gap, and a resistor, etc.,which are implanted on a mounting substrate 941 with wiring incorporatedinside thereof or on the surface thereof. Note that the “the members arearranged on the front end side (rear end side) of the case 91” means astate that a major part of the members, for example, 80% or more of themembers are arranged on the front end side (rear end side) of L/2, whenthe tube axial length of the case is set to L.

A connector 95 is disposed on the front end side of the lower space 922of the case 91, so as to partially protrude from the case 91. Theconnector 95 is electrically connected to a support wire 35 led out tothe internal space of the main body part 911. Note that the connector 95needs not to be formed by a separate member, and may be formedintegrally with the case 91. Further, the connector 95 may be formed onthe mounting substrate or as apart of the mounting substrate.

Further, a second circuit element group 933 for supplying a rated powerto the burner BN, is arranged on the rear end side of the lower space922. The second circuit element group 933 is constituted of a capacitor,a resistor, a switching element, a diode, and a microcomputer, etc.,which are implanted on a mounting substrate 942 with wiring incorporatedtherein. Note that the capacitor in the second circuit element group 933is particularly disposed on the rear end side of the lower space 922.

A shield case 96 for shielding an electromagnetic noise, is providedaround the case 91 including these circuit elements, etc. The shieldcase 96 is constituted of a case 961 and a case 962, which areintegrally engaged with each other. For example, aluminum can be used asthe shield case 96.

A circuit structure of the discharge lamp device of this embodiment isshown in FIG. 20. The discharge lamp device is constituted of a circuitpart CR including the connector 95, the second circuit element group933, and the first circuit element group 932, and the burner BN, whereinthe connector 95 portion is connected to the DC power supply DS such asa battery, via the switch SW.

The second circuit element group 933 is constituted of a DC/DC convertercircuit 9331, a voltage detecting circuit 9332, a current detectingcircuit 9333, a DC/AC inverter circuit 9334, and a control circuit 9335.The DC/DC converter circuit 9331 is a boost chopper circuit to boost andoutput a DC voltage of the DC power supply DS. A step-up transformer isdisposed in this DC/DC converter circuit 9331, and the step-uptransformer also functions as a transformer 931 that generates thehigh-voltage pulse for starting the burner BN, together with the firstcircuit element group 932. The voltage detecting circuit 9332 and thecurrent detecting circuit 9333 are respectively the circuits fordetecting an output voltage and an output current of the DC/DC convertercircuit 9331. The DC/AC inverter circuit 9334 is a bridge circuit forconverting DC to AC, and outputting the converted current. The controlcircuit 9335 is a circuit for controlling the DC/DC converter circuit9331 and the DC/AC inverter circuit 9334 so that a prescribe rated poweris input to the burner BN based on a detection result of a voltage valueand a current value detected by the voltage detecting circuit 9332 andthe current detecting circuit 9333.

The first circuit element group 932 is a circuit for generating thehigh-voltage pulse required for starting the lamp and starting theburner BN, in cooperation with the transformer 931 which is formed as apart of the aforementioned boost transformer.

With this circuit structure, in the circuit part CR, the high-voltagepulse of around 30 kV is generated for starting the burner BN, andimmediately after starting the burnet BN, power of 65 W to 75 W which ismore than twice the power of a steady time is generated, and power of 25to 35 W is generated in a steady time, and the power thus generated issupplied to the burner BN.

Then, the following test was carried out. Namely, the lighting circuitcombined type vehicle discharge lamp device of this embodiment wasattached to the reflector as shown in FIG. 12, and the lamp was lightedwhile vibrating the whole body of the device. As a result, it wasconfirmed that there was less positional fluctuation of the dischargearc formed between the pair of electrodes 32 while being lighted even ifthe whole body of the device was vibrated, and failure in lightdistribution could be avoided. This is because a weight balance in thetube axial direction of the discharge lamp is improved by disposing thetransformer 931 heavy in weight on the front end side and on the upperspace 921 side of the case 91, in the socket part 9111 that functions asa fulcrum in a state of the vehicle discharge lamp device. Thus, aneffect of generating less positional fluctuation of the discharge arceven if the device is vibrated, is meaningful in the discharge lamp notsealing mercury that easily allows the light distribution to be changedeven in a case of a slight fluctuation of the discharge arc caused bythinning of an arc.

Further, in order to further improve the weight balance and reduce aweight bias in upper and lower parts of the discharge lamp device, theconnector 95 with a harness mounted thereon, is disposed on the frontend side and the lower space 922 side. This would contribute tosuppressing the failure in light distribution. To summarize, thelighting circuit combined type discharge lamp device including theigniter circuit and the ballast circuit involves a problem that theweight balance of the discharge lamp device is poor, because the weighton the circuit side is increased, and the position of the arc formedbetween electrodes while being lighted is easily changed by vibration,etc. However, such a problem is solved by this embodiment.

Further, in the discharge lamp device of this embodiment, the firstcircuit element group 932 and the second circuit element group 933 arearranged on the rear end side of the case 91 which is long in the tubeaxial direction. Therefore, there is an advantage that the service lifeof the circuit element is prolonged. This is because increase of thetemperature of the circuit element can be suppressed by keeping thedistance between the circuit elements, and the light emitting part 11and the transformer 931 whose temperatures are increased while beinglighted. Note that when the mounting substrate 942 is disposed along thetube axial direction as shown in this embodiment, it is most suitable todispose the capacitor of the first circuit element group 932 which islarge in size and sensitive to heat, particularly on the rear end sideof the case 91 (for example, the rear end side of L/4). Incidentally,the first circuit element group 932 and the second circuit element group933 are relatively light in weight, and therefore even when they aredisposed on the rear end side of the case 91, there is almost noinfluence on the weight balance.

Accordingly, according to this embodiment, the weight balance in thetube axial direction is improved by constituting the circuit part CR bythe case 91, the transformer 931, the first circuit element group 932for generating the high-voltage pulse using the transformer 931 andstarting the burner BN, the second circuit element group 933 forsupplying the rated power to the burner BN, and the connector 95disposed in such a manner as protruding from the case 91, and bydisposing the transformer 931 on the front end side in the case 91.Therefore, even if the vibration is added to the discharge lamp device,the positional fluctuation of the discharge arc formed between a pair ofelectrodes 22 while being lighted, can be suppressed, and the failure inthe light distribution can be suppressed. Note that the shape of thecase 91 is not limited to a long shape in the tube axial direction.Further, the transformer 931 is not limited to one, and there may be aplurality of transformers. In this case, the transformer for generatingthe high-voltage pulse for starting the burner BN may be disposed atleast on the front end side of the case 91.

The weight balance in the tube axial direction is improved, and theupper and lower weight bias can be reduced, and also failure in thelight distribution can be suppressed by forming the space dividing wall9112 for dividing the internal space into the upper space 921 and thelower space 922 in the case 91, and disposing the transformer 931 on thefront end side and on the upper space 921 side in the case 91, anddisposing the connector 95 on the front end side and on the lower space922 side in case 91.

Further, the service life can be prolonged because the distance betweenthe heat source and the circuit elements can be kept, by disposing thefirst circuit element group 932 and the second circuit element group 933on the rear end side in the case 91.

Further, by disposing the capacitor included in the second circuitelement group 933 on the rear end side and on the lower space 922 sidein the case 91, the distance between the light emitting part 11 and thetransformer 931 becomes longer. Therefore, failure of the capacitor,which is sensitive to heat, can be prevented.

(Fifth Embodiment)

FIG. 21 is a sectional view of alighting circuit combined type vehicledischarge lamp device according to a fifth embodiment of the presentinvention.

In this embodiment, the space dividing wall 9112 is extended up toapproximately half of the case 91 in the longitudinal direction, and themounting substrate 943 on which the circuit element group 934 ismounted, is disposed on the rear end side of the case 91 approximatelyvertical to the tube axis, wherein the circuit element group 934 isconstituted of the first circuit element group and the second circuitelement group. With this structure, a layout of the wiring is moresimplified than that of the first embodiment, and therefore the circuitelement group 934 can be easily assembled into the case 91. Note thatwhen the mounting substrate 943 is disposed vertically to the tube axislike this embodiment, it is best suitable to dispose the capacitor onthe rear end side of the case 91 and on the lower space 922 side of thecase 91, to reduce an influence of heat. Further, in this embodiment,the circuit elements may be partially shared by the igniter and theballast, to thereby reduce the number of circuit elements.

(Sixth Embodiment)

FIG. 22 is an overall view of a vehicle discharge lamp according to asixth embodiment of the present invention.

In this embodiment, a conductive coating film 10 is formed on a surfaceof a sealing part 12 installed on the high-voltage side of the vehicledischarge lamp as described in the first and second embodiments. Withthis structure, startup performance can be improved as will be describedlater in detail.

The conductive coating film 10 is preferably formed of a material havingconductivity and hardly reacting with oxygen, etc., and for examplegold, oxide of indium, oxide of tin, oxide of zinc, ITO as oxide ofindium and tin, AZO obtained by doping zinc oxide with aluminum oxide,GZO obtained by doping zinc oxide with gallium oxide, or the like, and amaterial obtained by doping them with fluorine, gallium, and antimony,etc., can be used. Further, the material is preferably selected so thatthe resistance of a coating film portion is about 106 Ω/cm or less, andpreferably 50 to 100 kΩ (a resistance value is a value obtained bymeasuring the surface of a film having thickness of 150 nm, by a testerwith inter-terminals set to 1.5 mm.). The resistance value of this partdepends on the thickness of the formed coating film, and although notdetermined only by selecting the material, the resistance value is aneffective index to be controlled in the aforementioned value, for easilycausing the barrier discharge to occur. In short, the material and acombination thereof used based on the concept of the present invention,can be suitably determined according to each element suggested in thisspecification.

Further, according to a conventional art (International PatentPublication No. 2007-093525), the conductive coating film 10 is formedin light emitting part and in the vicinity of the light emitting part,thus involving a problem that there is an adverse influence on lightemitting characteristics such as total light flux unless a transparentmaterial is selected as the material constituting the coating film 10.However, in the discharge lamp according to this embodiment, theconductive coating film 10 is formed only around the metal foil 31 whichdoes not emit light in a steady time, and therefore the material needsnot to be a transparent material. Further, the conductive coating film10 is formed at a distance sufficiently far from the light emitting part11, and therefore there is less influence caused by heat, etc. Namely,the discharge lamp of this embodiment is also excellent in a point thatthe material can be relatively freely selected based on a condition thatthe startup characteristics can be improved.

An action of the discharge lamp of the present invention will bedescribed next.

When a high voltage is applied to the lamp, a lot of electrons aredischarged to the closed space 51 from the conductive coating film 10formed in the sealing part 12, to thereby electrify the closed space 51.At this time, a potential difference is generated in the conductivecoating film 10 and the closed space 51, thus causing discharge to occurat a low voltage. Owing to such a discharge, polarization and aphotoelectric effect occur inside/outside a surface of the inner tube 1,resulting in the dielectric breakdown of the electrodes 32.

An action for reducing the voltage required for startup is describedabove. However, corresponding effects can be exhibited even by aconventional technique of coating the light emitting part with aconductive coating film, in the meaning that the dielectric breakdownbetween electrodes is promoted by simply utilizing the discharge in theclosed space. However, it is found by the inventors of the presentinvention, that according to the conventional technique of forming theconductive coating film around the light emitting part, the startupcharacteristics are deteriorated in a period of a product service life.This is because circumference of the light emitting part is an extremelyhigh temperature zone while being lighted, thus vaporizing theconductive coating film which is formed immediately outside thereof, anddamaging a function of performing auxiliary discharge, and in additionchanging an atmosphere of the closed space, with components of theconductive coating film as impurities, and hardly allowing the dischargeto occur.

Accordingly, it is desirable to restrict a range so as not to form theconductive coating film 10 in the light emitting part 11 and in thevicinity of the light emitting part 11 (for example, a neck part of aboundary between the light emitting part and the sealing part).

More specifically, for example, the temperature of the vicinity of acenter of the metal foil 31 is lower than the temperature of the lightemitting part 11, and therefore the aforementioned problem can beprevented by forming the conductive coating film 10 with this part as areference. Further, it is a matter of course that the conductive coatingfilm may be formed at a position farther away from the light emittingpart 11, within an allowable space.

Note that as the distance between the conductive coating film 10 and themetal band 71 is set to be shorter, the startup performance can beimproved. As shown in FIG. 23, the startup voltage is reduced, as thelength in the tube axial direction from the end portion on the tip endside of the lamp of the metal band 71, up to the socket 5 side endportion of the conductive coating film 10, namely the distance c′between the conductive coating film 10 and the metal band 71 is shorter.According to FIG. 23, the distance c between the conductive coating film10 and the metal band 71 is set to 3.5 mm or less, and preferably set to2.0 mm or less, to thereby make the startup performance excellent.

In addition, further high effect can be expected by setting both thedistance c between the metal foil 31 and the metal band 71, and thedistance c′ between the conductive coating film 10 and the metal band71, at suitable positions.

As shown in FIG. 24, although the startup performance is reduced only byshortening the distance c′, the startup performance is further reducedby shortening the distance c as described in the second embodiment.Thus, the distance c between the metal foil 31 and the metal band 71 ispreferably set to 2.0 mm or less, and the distance c′ between theconductive coating film 10 and the metal band 71 is preferably set to3.5 mm or less.

Here, specifically, the conductive coating film 10 of this embodiment isformed by four circular dots so as to be partially overlapped, as shownin FIG. 25. The material is tin oxide, a film thickness is 100 nm, anarea is 10 mm², and a length of an edge is 14 mm. Thus, by forming theconductive coating film 10 by combining a plurality of geometric shapes,a total circumference of the conductive coating film 10 can besufficiently large in the limited space, and therefore the startupperformance can be improved. Of course, not only a plurality of samegeometric shapes may be combined, but also a plurality of differentgeometric shapes may be combined. For example, a conductive coating filmformed by combining circles and squares can also be employed.

Although according to the present invention, a forming method of theconductive coating film 10 is not particularly limited, a plurality ofdot patterns as shown in FIG. 25 can be formed, for example, byrepeatedly performing a process of dropping a liquid material to thesealing part 12 of the inner tube, at varied positions. According tothis method, the conductive coating film with desired film thickness andarea can be formed by suitably adjusting a viscosity of the materialitself and a height of drop when a coating film material is droppedusing a publicly-known dispenser. Thus, it is a matter of course thatthe method for forming a desired shape can be employed by a scientificmethod such as etching or vapor deposition by masking, in addition to aprocess of utilizing a diffusion of the material itself.

FIG. 26 is a graph for plotting actually measured values obtained byexamining a relation between areas of the conductive coating film and adrop rate of the startup voltage, with areas of the conductive coatingfilm varied, and the areas of the conductive coating film being formedin the sealing part. As is clarified from this graph, reduction of 20%or more of the startup voltage is achieved by forming the conductivecoating film with an area of 3 m² or more, compared with a case that theconductive coating film is not formed (=0 mm²).

Further, when the test was carried out repeatedly, with conditionschanged, it was found that not only the area but also other elements hadan influence on the effect of reducing the startup voltage, depending onthe shape of the conductive coating film. For example, even in a case ofthe coating film with same area, when a coating film of a perfectcircle, and a coating film of a star shape with outer edge formedirregularly, were compared, it was confirmed that the latter was capableof easily starting the lamp. It can be considered that this is becausefield concentration occurs in the vicinity of an outer peripheral edgeportion of the coating film, and the outer edge becomes a start point ofthe auxiliary discharge. Therefore, a part to be the start point isincreased by making the outer periphery longer. Accordingly, it can besaid that in order to achieve a sufficient auxiliary discharge by arequired minimum amount of the conductive coating film, a complicatedshape such as a combination of a plurality of geometric shapes ispreferable, rather than a simple shape such as a square or a perfectcircle.

Based on such knowledge, it can be said that the present invention caninclude various modified embodiments as the embodiments of theconductive coating film formed in the sealing part. Illustrated in FIG.27 are some of these embodiments.

For example, a conductive coating film 10 a shown in (a) is formed insuch a manner that two circular dots are partially overlapped in zigzag.Wherein, the “dot” called in this specification is not limited to thecircle shown in the figure, and for example, it should be interpreted asa concept including ovals, squares such as a rectangle and polygons suchas a hexagon, and shapes including irregular shapes such as a star orapproximately the star. Namely, as is understood from an ordinarymeaning of the “dot”, it can be said that the coating film sufficientlysmaller than a width of the sealing part 12, for example, covering thewhole body of the sealing part 12, and extending to the neck part of theboundary between the sealing part 12 and the light emitting part 11, isexcluded from the concept of the “dot” called in this specification.

A conductive coating film 10 b of (b) is formed by forming two circulardots at positions opposed to the metal foil 31 respectively. In thiscase, when a prescribed startup voltage is applied, the dielectricbreakdown is assisted, with either one of the two coating films set as astart point.

A conductive coating film 10 c of (c) is formed so that three oblongrectangular films are formed in parallel to a width direction of themetal foil 31. In a case of the conductive coating film 10 c with smallwidth, field concentration easily occurs at a startup time, andtherefore startup at a low voltage is enabled. Note that it isadvantageous if the width is smaller, and for example, when the width is2 mm or less, the startup voltage can be improved by about 1.5 kV,compared with a case that the conductive coating film is simply formedinto a rectangular shape.

A conductive coating film 10 d of (d) is formed having zigzag edge, bybeing formed into a shape combining a plurality of acute-angledtriangles on the end portion. With such a shape, a peripheral length canbe tremendously long, more than that of the rectangular conductivecoating film with same area. Further, the field concentration occurs atan acute end portion, to thereby enable startup at a low voltage.

Not that in the aforementioned various embodiments, explanation is givenfor an embodiment that the conductive coating film is arranged to facean interface between the electrode and the metal foil. However, thepresent invention is not limited to this embodiment. Namely, althoughthe effect of the auxiliary startup is considered to be relatively highgenerally in a case of a small distance between the metal foil and theconductive coating film, as shown in FIG. 27( c) to FIG. 27( d), theeffect of the auxiliary startup can be obtained by forming theconductive coating film on an opposite side to the sealing part, andfurther by forming the conductive coating film on both sides. Therefore,in the present invention, which side face of the sealing part is used toform the conductive coating film is not limited, in relation to themetal foil. Further, the conductive coating film 10 may be formed so asto be shifted in a longitudinal direction of the metal foil 31,irrespective of the aforementioned positional relation, and one of theconductive coating films 10 may be formed into a shape different fromthe shape of the other one.

Further, the present invention is described as the invention that can beapplied to the mercury-free discharge lamp substantially not containingmercury as a discharge medium. However, it is no problem in utilizingthe present invention similarly in the discharge lamp containingmercury. Namely, it is a general matter that in the mercury-free lamp,the pressure in the discharge space is high, and inter-electrodedistance is large, thus requiring further high startup voltage.Accordingly, it can be said that usefulness of the present invention ishigh, which is capable of reducing the startup voltage. However, thereis no problem in applying the present invention to the discharge lampwith mercury, for the similar purpose of improving the startupcharacteristics.

(Seventh Embodiment)

FIG. 28 is a view of a vehicle discharge lamp according to a seventhembodiment of the present invention, wherein (a) is an expanded view ofthe vicinity of a sealing part, and (b) is a view of a sectional facetaken along the line X-X′ shown by one dot chain line, viewed from adirection of arrows.

In this embodiment, a conductive coating film 10 e is formed, includinga protuberance 10 e 1 on the end portion, and a planar portion 10 e 2formed so as to be surrounded by the protuberance 10 e 1. Morespecifically, 7 mm² of the conductive coating films 10 e arerespectively formed on front and rear surfaces where the metal foil 31of the sealing part 12 positioned at the high-voltage side, with a filmthickness of the protuberance 10 e 1 being T1=0.00035 mm, and a filmthickness of the planar portion 10 e 2 being T2=0.00015 mm. Thus, byforming the protuberance on the conductive coating film 10 e, withhigher height than a height of the planar portion extending in adirection approximately vertical to a surface, field concentrationoccurs in the protuberance 10 e 1 at the time of applying the startupvoltage, thus easily generating the dielectric barrier discharge.Therefore, the startup performance can be more improved than a case thatthe conductive coating film 10 e is simply formed into a planar shape.

The conductive coating film 10 e including such a protuberance 10 e 1,can be formed by dropping a conductive solution by a dispenser, etc.,the conductive solution being obtained by mixing tin oxide and butylacetates adjusted to obtain a low surface tension, and aftersufficiently spreading this solution on the sealing part 12, applying asintering process thereto using a hydrogen burner, etc. After sintering,most of the components of the butyl acetates are jumped, thus making itpossible to obtain a conductive coating film with high transparency anda resistance value of about 100 kΩ.

Note that according to this embodiment, a pattern 311 is formed on ahalf surface of the electrode 32 side of the surface of the metal foil31, for suppressing the generation of a crack leak. The pattern 311 isformed by a plurality of non-penetrating semi-circular recesses arrangedby irradiation of YVO4 laser for example. Namely, minute irregularitiesare formed on the surface of a foil as is described in WO2008/129745A1and WO2007/086527A1, etc. Thus, by forming the conductive coating film10 e in the sealing part 12 so as to include the surface of the pattern311, the polarization immediately after startup is promoted by theirregularities of the pattern 311, and therefore further improvedstartup performance can be expected.

Regarding a conventional lamp (called conventional embodiment 1hereafter) in which a conductive film with a uniform film thicknesssimilarly to the lamp of this embodiment (called embodiment 1 hereafter)is formed, whether the lamp was started or not was tested, using alighting circuit that continuously outputs a voltage waveform withstartup pulse voltage=23 kV, and rise time=250 nsec. As a result, it wasfound that the startup voltage of the lamp of the embodiment 1 had atendency of reducing the startup voltage rather than the lamp of theconventional embodiment 1. Further, as a result of carrying out the testby increasing the number to 200, it was found that the lamp withinferior startup performance among the tested lamps of the conventionalembodiment 1 had a startup pulse voltage of about 18 kV, and meanwhilethe lamp of the embodiment 1 had a startup pulse voltage of about 16 kV,even in a case of a lamp with inferior startup performance. Therefore,it can be said that startup variation is small and lighting failure issmall in the lamp of the embodiment 1.

Next, test was carried out for the variation of the startup voltage whenthe relation T1/T2 between the film thickness T1 of the protuberance 10e 1 and the film thickness T2 of the planar portion 10 e 2 was varied.Results thereof are shown in FIG. 29. Note that the number of tests is200 respectively, and both the film thicknesses T1, T2 are the thicknessof an average part when the film thickness is not constant.

As is clarified from FIG. 29, it is found that as T1/T2 are larger, anaverage value and a worst value (maximum value of variation) are likelyto be small, and particularly the range of T1/T2≧2 is preferable.Namely, a conductive coating film 9 is preferably formed so as tosatisfy T1/T2≧2. However, not so much variation is observed in thestartup performance in a range of T1/T2≧2. Therefore, T1/T2 ispreferably 5 or less, and further preferably 3 or less, in considerationof easiness in manufacture.

In addition, the protuberance 10 e 1 is not limited to theaforementioned embodiment, and a size and a place can be changed. Forexample, as shown in FIG. 30( b), which is a view of a sectional face ofFIG. 30( a) taken along the line Y-Y′ by one dot chain line, aprotrusion 121 is formed in the sealing part 12, and the surface of thesealing part 12 is coated with the conductive coating film 10 e so as toinclude the protrusion 121, to thereby form the protuberance 10 e 1 in apart other than an edge portion of the conductive coating film 10 e.

(Eighth Embodiment)

FIG. 31 is a view for describing a vehicle discharge lamp according toan eighth embodiment of the present invention, wherein (a) is anexpanded view of the vicinity of a sealing part and (b) is an expandedview of one dot chain line Z.

In this embodiment, a sawteeth part 10 e 3 including a plurality ofprotrusions protruded to outside in a width direction of a film havinga—plurality of burrs like sawteeth, is formed on an edge portion of theconductive coating film 10 e. Thus, by forming the sawteeth part 10 e 3on the edge portion of the conductive coating film 10 e, fieldconcentration easily occurs in the tip end portion thereof. Therefore,the dielectric barrier discharge is easily generated at the time ofstartup. Further, the length of the edge of the conductive coating film10 e becomes long, and therefore the startup performance can be improvedby forming the sawteeth part 10 e 3 on the edge portion of theconductive coating film 10 e. The conductive coating film 10 e includingthe sawteeth part 10 e 3 on the edge portion as described above, can beformed by increasing a height of drop of the conductive solution.

In addition, it is best suitable to form the conductive coating film 10e in a crown shape having both the protuberance 10 e 1 and sawteeth part10 e 3 as shown in FIG. 32. In this case, the startup voltage can bedecreased by about 4 kV, compared with a case of a coating film which isformed into a plane shape, with smooth edge, and having same area. Notethat tip end portions of the protuberance 10 e 1 and the sawteeth part10 e 3 have a pointed shape rather than an arc shape respectively,preferably at an acute angle rather than an obtuse angle. In addition,further much forming numbers are preferable. By employing them, thefield concentration further easily occurs, and therefore the startupperformance can be further improved.

(Ninth Embodiment)

FIG. 33 is a view for describing a vehicle discharge lamp according to aninth embodiment of the present invention.

In this embodiment, a conductive coating film 10 f made of ITO havingfilm thickness=10 nm is formed on an inner surface of the outer tube 5in the vicinity of the sealing part 12 on the high-voltage side. Whenthe conductive coating film is formed in the outer tube 5, the potentialdifference between a glass portion of the sealing part 12 and the outertube 5 portion is increased. Therefore, the startup performance can beimproved. Note that the conductive coating film 10 f can be formed, forexample, by a method of sucking the conductive solution into the outertube 5 and drying the sucked conductive solution, and thereafterremoving an unnecessary portion.

(Tenth Embodiment)

FIG. 34 is a view for describing a vehicle discharge lamp according to atenth embodiment of the present invention.

In this embodiment, a conductive coating film 10 f is formed on theinner surface of the outer tube 5 in the vicinity of the sealing part 12on a low-voltage side, and a conductive coating film 10 g is formed onthe sealing part 12 on the high-voltage side. Note that the conductivecoating film 10 g has a structure that a recess portion 122 is formed ina sealing part 11, and a coating film is formed on the recess portion122. Thus, a distance between the conductive coating film 10 g and themetal foil 31 becomes near, and therefore further high effect can beexpected and also the range and the thickness of a film can be easilycontrolled, thus making it possible to reduce a variation incharacteristics. In addition, there is also an advantage that the stepof forming the coating film can be facilitated.

A discharge startup voltage of the lamp having this structure is 13.3kV, and the effect of improving the startup performance is remarkableeven if being compared with the discharge lamp of other embodiment. Itcan be considered that the aforementioned remarkable effect of theimprovement in startup is influenced by the generation of the dielectricbarrier discharge in the vicinity of the light emitting part 11, whichis caused by forming the conductive coating film 10 g on the highpressure side sealing part 12, and forming the conductive coating film10 e on the inner surface of the outer tube 5 in the vicinity of the lowpressure side sealing part 12. Accordingly, when the conductive coatingfilm is formed in inner/outer tubes respectively, it may be formed tograsp the light emitting part 11, so that the dielectric barrierdischarge is generated in the vicinity of the light emitting part 11.

(Eleventh Embodiment)

FIG. 35 is a view for describing a vehicle discharge lamp deviceaccording to an eleventh embodiment of the present invention.

In this embodiment, a high-voltage pulse of negative polarity is appliedto the high-voltage side sealing part having a conductive coating filmformed thereon. With this structure, the generation of the dielectricbarrier discharge can be assisted as will be described later, andtherefore startup variation of the lamp can be reduced. The“high-voltage pulse of negative polarity” means the pulse generated onthe negative side immediately after application, as shown in FIG. 35.Whereby, whether the polarity is negative polarity or positive polaritycan be judged by observing a waveform obtained by connecting anoscilloscope OS to a circuit portion connected to the high-voltage sideof the lamp. Note that in this embodiment, a peak value of a pulsewave=24 kV, being a fall time, namely, the time of a high-voltage pulserequired for changing the pulse waveform to 10% to 90% of the peak valueof the pulse wave, expressed by the time of the high-voltage pulse=110ns. Such a pulse can be generated by reversing a winding direction ofthe transformer.

Regarding a plurality of discharge lamp devices of this embodiment(embodiment 2, hereafter), and a plurality of discharge lamp devices forapplying high-voltage pulse of positive polarity (conventionalembodiment 2, hereafter) respectively, a test for measuring the startupvoltage and a variation thereof, was carried out. Results thereof areshown in FIGS. 36( a) and (b).

As is clarified from the results, an average value of the startupvoltage is equal in both the embodiment 2 and the conventionalembodiment 2, or slightly smaller in the conventional embodiment 2.However, as is clarified from a value of a standard deviation, thestartup voltage is smaller in the embodiment 2. This is because byapplying the high-voltage pulse of negative polarity, γ-effect ofdischarging secondary electrons from the surface of the conductivecoating film can be obtained. Namely, in the embodiment 2, thegeneration of the dielectric barrier discharge is assisted. Therefore,it can be considered that the probability of startup is increased, andthe variation is reduced. When the startup variation is thus reduced,there is no necessity for designing a transformer with good margin inoutput of the pulse, and therefore miniaturization of the transformerand reduction of a cost are achieved. Note that further high effect canbe expected when the conductive coating film is formed on both sides ofthe sealing part.

FIG. 36( a) shows a startup voltage distribution when a high-voltagepulse of positive polarity is input, and (b) shows a startup voltagedistribution when the high-voltage pulse of negative polarity is input,into a lamp without conductive coating film. As is clarified from theresults, even if the high-voltage pulse of negative polarity is inputinto the lamp without conductive coating film, both the startup voltageand the variation are poorer than a case of the high-voltage pulse ofpositive polarity. Therefore, in the discharge lamp without conductivecoating film, it is general that the high-voltage pulse of positivepolarity is supplied. In the lamp in which gas is sealed in the spaceand which has the conductive coating film formed on the surface of thehigh-voltage side sealing part, it can be said that the structure ofinputting the high-voltage pulse of negative polarity is unexpected andalso results of FIG. 36( a) are unexpected.

Next, the variation of the startup voltage was tested, with the falltime varied, which is the fall time of the high-voltage pulse ofnegative polarity applied to the lamp. As a result, it was found thatthe average startup voltage and the variation were varied depending onthe fall time. For example, as shown in FIG. 38, when the high-voltagepulse with fall time of about 300 ns was applied, although the averagevalue of the startup voltage was slightly decreased compared with a casethat the fall time was about 110 ns, the standard deviation wasincreased by 1.5 times. Namely, when a startup variation is reduced, itis suitable to set the fall time shorter, and therefore from the resultsof various tests, the fall time of the high-voltage pulse of negativepolarity, is preferably set to 180 ns or less, and further preferablyset to 110 ns or less.

Note that this embodiment is further effective by combining it with thefollowing structure.

(A) Argon is sealed in the space 51.

When argon and nitrogen are compared, argon is easily ionized. Namely,argon is the gas having low ionizing energy, and therefore when thehigh-voltage pulse of negative polarity is applied at a startup time, adischarge amount of the secondary electrons is increased, and thedielectric barrier discharge is easily generated. Note that rare gassuch as neon and xenon corresponds to the gas with low ionized energy.However, neon easily escape from the space 51 during its service lifewhen the temperature of the light emitting part 11 is excessivelydecreased, and xenon and krypton are not suitable for a practical use,because the temperature of the light emitting part 11 is excessivelyincreased. Meanwhile, it is most suitable to use argon, because argon iscapable of further improving the startup performance by γ-effect, whilemaintaining the temperature of the light emitting part 11 to be uniform.Note that argon is not limited to a single body, and when a major part,for example, 90% or more of the whole body is occupied by argon, it canbe said that argon is most suitable to be used. Further, the pressure ofgas is preferably set to 0.3 atm or less, and further preferably set to0.1 atm or less.

(B) Combination with conductive coating films as shown in the seventhand eighth embodiments.

When combined with the conductive coating film including theprotuberance and/or the sawteeth part as shown in FIG. 32, thedielectric barrier discharge is easily induced by an increase of aconcentration of electrons under γ-effect, and by the fieldconcentration on the tip end portion of the conductive coating film, andtherefore the startup performance is improved.

(C) High-voltage pulse of positive polarity is applied to one of theelectrode mounts 3, and high-voltage pulse of negative polarity isapplied to the other electrode mount 3 at a startup time (called bothhigh-voltage startup hereafter).

As shown in FIG. 39, with a structure of the both high-voltage startup,the circuit can be miniaturized and insulation can be easily secured,while maintaining excellent startup performance. For example, when thehigh-voltage pulse is applied only to one side, and in a case of thelamp requiring high-voltage pulse of 20 kV for startup, the lamp isstarted only by applying 10 kV of the high-voltage pulse to one side,which is about half of 20 kV, and therefore two transformers with smalloutput can be substituted therefore. Since such a transformer is smallin size, a degree of free design of an arrangement of circuit members isincreased, and the insulation can be easily secured, thus realizing acost reduction. Such an advantage is meaningful in a case that the sizeis limited in a device, such as a lighting circuit combined type vehicledischarge lamp device as shown in FIG. 19. Note that when the structureof both high-voltage startup is employed, it is most suitable to employa waveform structure in which only polarity is inverted while the phaseis same.

Here, peak values of the high-voltage pulse of positive/negativepolarities are not necessarily the same values, and may be changed asdesired, like the peak value of the high-voltage pulse satisfying thepeak value of a 1^(st) side (socket side) high-voltage pulse>the peakvalue of a 2^(nd) side (support wire side). In a case of the vehicleheadlight, a metal member called a shade for controlling lightdistribution is disposed in the vicinity of the tip end portion of thelamp, thus involving a problem that when the high-voltage pulse isapplied to the support wire 34 side, the voltage leaks to the shade.However, if the rate of the peak value of the high-voltage pulse on the2^(nd) side (support wire side) is decreased, generation of the leak canbe suppressed.

The present invention described above can be utilized as an illuminationdevice for various purposes of use, such as vehicle headlamp, fog lamp,and other vehicle illumination or outdoor lamp, capable of achieving thelight emission efficiency and service life characteristics equivalent tothose of a conventional product, while achieving low power consumption.

The invention claimed is:
 1. A vehicle discharge lamp substantially notusing mercury, comprising: a light emitting part in which a dischargespace is defined and into which a discharge medium including metalhalide and rare gas are sealed; and a pair of electrodes arranged in thedischarge space, wherein a spherical length b, which is a length in atube axial direction of the light emitting part, is 7.5 mm to 8.5 mm anda thickness volume V of the light emitting part is 50 mm³ to 100 mm³,and wherein the following formula is satisfied:−20≦(a−35)×5.5+(x−13.5)×10+(1.85−t)×100+(2.5−d)×100≦20 wherein a: power[W] supplied in a stable lighting time, satisfying:22<a≦26 x: pressure [atm] of rare gas sealed in the discharge space andranging 10˜17 atm t: thickness [mm] of a part where a wall thickness ofthe light emitting part is maximum and ranging 1.3˜1.85 mm d: innerdiameter [mm] of a part where the wall thickness of the light emittingpart is maximum.
 2. The vehicle discharge lamp according to claim 1,wherein the electrodes are thoriated tungsten electrodes containing 0.1wt % to 0.5 wt % of thorium oxide.
 3. The vehicle discharge lampaccording to claim 1, wherein an outer tube is provided to cover thelight emitting part, gas is sealed in a closed space formed between thelight emitting part and the outer tube, heat conductivity λ of the gasis 0.01 to 0.03 W/m·K, and a distance D between a part where an outerdiameter of the light emitting part is maximum and an inner surface ofthe outer tube is 0.5 to 1.0 mm.
 4. The vehicle discharge lamp accordingto claim 1, wherein metal foils are sealed to sealing parts formed onboth ends of the light emitting part, a metal member is provided on anouter peripheral surface of an outer tube which is provided to cover thelight emitting part, with a closed space formed between them filled withgas, and a distance c in a tube axial direction between the metal foilsand the metal member is 2.0 mm or less.
 5. The vehicle discharge lampaccording to claim 1, further comprising: an inner tube having a sealingpart and a light emitting part having a discharge space inside; adischarge medium sealed into the discharge space; an electrode mountair-tightly sealed to the sealing part; and an outer tube provided tocover the light emitting part, wherein a closed space formed between theinner tube and the outer tube is filled with gas, and a conductivecoating film is formed on a surface of the sealing part.
 6. The vehicledischarge lamp according to claim 5, wherein a metal member is providedon an outer peripheral surface of the outer tube, and a distance c′between the conductive coating film and the metal member is 3.5 mm orless.
 7. The vehicle discharge lamp according to claim 5, wherein theelectrode mount includes a metal foil air-tightly sealed to the sealingpart, and the conductive coating film extends at least along a surfaceopposed to the metal foil, in a form that a plurality of geometricshapes are combined.
 8. The vehicle discharge lamp according to claim 5,wherein the conductive coating film includes at least one of: aprotuberance with a film thickness formed to be large and, a sawteethpart including a plurality of protrusions on an edge portion in such amanner as protruding to outside in a width direction of a film.
 9. Avehicle discharge lamp device, further comprising: the vehicle dischargelamp according to claim 5; and a lighting circuit for lighting thevehicle discharge lamp, wherein in the lighting circuit, a high-voltagepulse of negative polarity is generated at a startup time, and thegenerated high-voltage pulse is applied to the discharge lamp.
 10. Avehicle discharge lamp device, further comprising: the vehicle dischargelamp according to claim 1; and a lighting circuit for lighting thevehicle discharge lamp, wherein the lighting circuit includes a ballastcircuit that outputs an AC current with a current slope of a zero crosscurrent being 0.05 A/μs or more while being lighted in a stable lightingtime from polarity inversion to a point when a current reaches 0.2 A,and a sectional area of a current that flows to the electrode of thedischarge lamp while being lighted in a stable lighting time, is 6 to 15A/mm².
 11. A lighting circuit combined type vehicle discharge lampdevice, further comprising: a burner of the vehicle discharge lampaccording to claim 1; and a circuit part that holds the burner on afront end side, wherein the vehicle discharge lamp is configured to belighted, with a tube axis set in approximately a horizontal state, thecircuit part further including: a case; a transformer; a first circuitelement group that generates a high-voltage pulse using the transformer,and starts the burner; a second circuit element group that supplies arated power to the burner; and a connector disposed in such a manner asprotruding from the case, wherein the transformer is disposed on a frontend side in the case.
 12. A lighting circuit for lighting the vehicledischarge lamp according to claim 1, further comprising: a ballastcircuit that outputs an AC current with a current slope of a zero crosscurrent being 0.05 A/μs or more while being lighted in a stable lightingtime from polarity inversion until a point when a current reaches 0.2 A.